The present invention relates to an ignition timing control system for internal combustion engines, which has a knocking decision level for each cylinder of an internal combustion engine.
Conventional knocking feedback systems detect a knocking from vibration noises or the like of an internal combustion engine. Upon detection of a knocking signal, the ignition timing is retarded by a certain angle, while in the absence of a knocking signal for a predetermined length of time, the ignition timing is advanced by a certain angle.
The conventional knock feedback systems are such that, in detecting a knocking, it is decided that a knocking has occurred and the ignition timing is retarded when the signal produced from a knocking detector exceeds a decision level set in the knock feedback system. Generally, the knocking detector provided on the internal combustion engine detects knockings of a plurality of cylinders. The vibration of a cylinder distant from the detector is more difficult to detect than the vibration of a cylinder closer to the detector, the distant cylinder producing a smaller detection signal. In other words, the ability to detect a knocking is dependent on the position of cylinders, with the result that the controllability of the ignition timing of a cylinder distant from the knocking detector is deteriorated. The ignition timing of a cylinder distant from the knocking detector is thus excessively advanced, so that the knocking is aggravated, thereby leading to the damage of the combustion chamber and the deteriorated engine operating efficiency.